This invention relates to a process for immunologically assaying glycolipid in an organism. Recently there has been observed in many countries a very high mortality rate due to cancer. The expectation, need of detection, and treatment for cancer in its early stage have become progressively greater. Morphological tests such as imaging diagnostic technology and immuno-biochemical diagnostic technology, which is a noninvasive test carried out by collecting a small amount of humors, have been used to detect cancer in its early stage. The role of the immunobiochemical diagnostic technology has become increasingly important. The following have been attempted to detect tumor associated antigens, the number of which would be remarkably increased by the proliferation of cancer cells; to diagnose cancer immuno-biochemically, which has resulted in the finding of .alpha.-fetoprotein, carcinoembryonic antigen and the like; and the development of assay systems thereof which are clinically useful in practice. However, these markers are not satisfactory from the viewpoint of an early diagnosis of cancer. Therefore it has been eagerly desired to find a novel tumer associated antigen as well as to develop an assay system and find clinical application thereof.
Turning attention to glycolipid which is one of the constituents of cell membrane, we have investigated the relationship between glycolipid and cell adhesion by analyzing glycolipid in cancerous cells and examining the metabolism thereof. Consequently we have found that the difference in cell adhesion might be represented by the difference in glycolipid metabolism. In particular, a biosynthetic pathway of glycolipid via another glycolipid which is seldom observed in a normal cell has been found in a highly malignant cancerous cell devoid of cell adhesion. That is to say, four different glycolipids have been found to increase with the proliferation of cancer cells. These glycolipids have been identified as asialo GM.sub.1, asialo GM.sub.2, fuco GA.sub.1 and paragloboside as a result of various analyses. The structures of these glycolipids are as follows:
asialo GM.sub.1, Gal-GalNAc-Gal-Glc-Cer; PA1 asialo GM.sub.2, GalNAc-Gal-Glc-Cer; PA1 fuco GA.sub.1, ##STR1## and paragloboside, Gal-GlcNAc-Gal-Glc-Cer
wherein Gal represents galactose, Glc represents glucose, Fuc represent fucose, GalNAc represents N-acetylgalactosamine, GlcNAc represents N-acetylglucosamine and Cer represents ceramide.
We have found that these glycolipids may be available as novel cancer markers, since they would increase in human cancerous cells and would therefore be extremely useful in cancer diagnosis by determining their concentrations in humors. We have further established a simple process for immunologically assaying these glycolipids with high sensitivity and accuracy. It has been hitherto impossible to clinically determine such a low concentration of these glycolipids in humors.